Electronic structure and indirect spin-spin interactions in bournonite (CuPbSbS3) according to antimony nuclear quadrupole resonance

A complex sulfide CuPbSbS₃ (bournonite) has been studied by the nuclear quadrupole resonance on ^121,123Sb. The temperature dependences of the spectroscopic and relaxation parameters in the temperature range of 10–295 K have been obtained. The crystallochemical features of the environment of the two non-equivalent Sb positions in the unit cell have been revealed from the nuclear quadrupole resonance spectra. The existence of the lattice vibrations with the frequency ω = 110 cm^?1 has been demonstrated on the basis of the temperature dependence of the nuclear quadrupole resonance frequencies. Slow beats have been observed on the decay curve of the spin echo signal. Experimental data have been analyzed in order to reveal the existence of the indirect spin-spin interactions involving Sb atoms. The indirect spin-spin coupling constant has been estimated as J = 2.5 ± 0.5 kHz.     

Structure and luminescence properties of antimony(III) complex compounds

The influence of the structure of the anion sublattice on the spectral luminescence properties is investigated using the example of antimony(III) complex compounds with outer-sphere organic cations. It is established that the factors favorable for the enhancement of the luminescence of antimony(III) ions are the island structure of the anion sublattice with minimum distortions of the antimony(III) coordination polyhedron and closely spaced energy levels of the outer-sphere organic cation and the antimony(III) ion.     

Superconductivity and magnetic fluctuations in Cd(2))Re(2)O(7) via Cd nuclear magnetic resonance and re nuclear quadrupole resonance

We report Cd nuclear magnetic resonance (NMR) and Re nuclear quadrupole resonance (NQR) studies on Cd(2)Re(2)O(7), the first superconductor among pyrochlore oxides (T(c) approximately 1 K). The Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below T(c) exhibits a pronounced coherence peak and follows the weak-coupling BCS theory with nearly isotropic energy gap. The results of Cd NMR point to a moderate ferromagnetic enhancement at high temperatures followed by a rapid decrease of the density of states below the structural transition temperature of 200 K.     

Homonuclear dipolar broadening of spin 5/2 pure nuclear quadrupole resonance line

An expression of the second moment due to the homonuclear dipolar broadening of a pure Nuclear Quadrupole Resonance (NQR) line, produced by an axially symmetric electric field gradient, on a nuclei system with spin 5/2 has been derived. A comparisons is made with previous results obtained for both spin 1 and 3/2.     

Nanostructural pulse laser-deposited Ag(Tl)SbS semiconductor thin films: Growth dynamics, structural and electrical properties

Ag₃SbS₃ semiconductor material is an attractive substance for different optoelectronic and data storage applications [D. Adler, M.S. Shur, M. Silver, S.R. Ovchinsky, J. Appl. Phys. 51 (1979) 3289]. The most reliable way to get thin films with proper quality is the pulse laser deposition (PLD) technology. The paper reports data on growth dynamics (electron microscopic experiments (EME) performed in situ in order to clarify structural features of the films under PLD process), X-ray diffraction (XRD) investigations and room temperature current-voltage (IVC) characteristics. The sets of investigated samples were prepared by Nd:IAG laser. Films were deposited under substrate temperatures T = 300 K and T = 400 K and at different pulse repetition frequencies. EME studies revealed time-dependent changes of the grown films’ structure occurring under stationary pulse repetition frequency and the substrate temperature. The structure of the films was identified as an amorphous with nanoscale crystalline phase inclusions (there are results of the XRD studies). The IVCs investigations performed at the room temperature and under applied bias up to 10 V in both directions showed a domination of tunneling current for all samples under study.     

Measurement of the (14)N nuclear quadrupole resonance frequencies by the solid effect

(1)H-(14)N nuclear quadrupole double resonance using magnetic field cycling between high and low magnetic field and solid effect in the low magnetic field is analyzed in details. The transition probabilities per unit time for the solid-effect transitions are calculated. The double resonance spectra are calculated in the limiting cases of fast and slow nitrogen spin-lattice relaxation. The double resonance spectra are measured in histamine and quinolinic acid. The experimental spectra are analyzed and the (14)N NQR frequencies are determined.     

Nuclear quadrupole resonance studies of209Bi in Bi4(GeO4)3 and Bi4(SiO4)3

Nuclear quadrupole resonance (NQR) of²⁰⁹Bi has been studied in Bi₄ (GeO₄)₃ and Bi₄ (SiO₄)₃ using a wide band coherence-controlled superregenerative oscillator-detector. All the four allowed (ΔM _I=±1) transitions are observed. In both cases the electric field gradient (EFG) tensor is axially symmetric (η=0.0). The quadrupole coupling constante ² qQ is measured to be 490.8±1 MHz and 470.4±1 MHz respectively. It is pointed out that the purely ionic model is inadequate to understand these results. With the available experimental accuracy and the strength of the applied electric field (∼ 6 KV/cm), no field-induced effects on the NQR spectrum could be observed in the case of Bi₄ (SiO₄)₃.     

Line shape analysis in nuclear quadrupole resonance spectroscopy (I=3/2)

Following the treatment of Vega (1973), the theoretical expressions for the second moments in nuclear quadrupole resonance (nqr) due to dipole-dipole interactions have been derived for the system containing the nuclei with spinI=3/2. Cases with the orientation of the static magnetic field and the interactions with the other magnetic nuclei are also dealt with.     

Structure and electronic properties of antimony films on the Mo(110) surface

The structure and electronic properties of antimony on the Mo(110) surface are investigated over a wide range of coverages. In the submonolayer range, p(2×1), p(1×1), (1×3), and (1×2) adsorbate structures matched to the substrate are formed at room temperature. For coverages larger than a monolayer, three-dimensional antimony crystals whose orientation is determined by the substrate grow on the surface. Annealing of the system at temperatures higher than 1000 K leads to the formation of structures that are not observed upon condensation. The results of analyzing the electron energy-loss spectra jointly with the work function of the surface suggest the formation of surface molybdenum-antimony alloys.     

A new approach to stroboscopic resonance measurements of the nuclear quadrupole interaction

A new stroboscopic resonance method for the measurement of the quadrupole interaction of long-lived nuclear isomers excited by pulsed beams with a fixed repetition frequency is demonstrated. The method utilizes the phenomenon of beats which occurs when a magnetic perturbation is introduced in the presence of a pure quadrupole interaction. The nuclear precession is thus controlled by the beat frequencies which can be varied by the external magnetic field which is oriented parallel to the symmetry axis of the crystal. Stroboscopic resonance can be achieved by varying thebeat frequency to be an integral multiple of the beam pulsing frequency. The method is demonstrated using the 398 keV level of⁶⁹Ge excited and recoil implanted into a single crystal of tin by means of a heavyion reaction.Supported in part by the National Science Foundation.     

Sodium-23 MAS NMR study on nuclear quadrupole interaction in NA(1-x)Ag(x)NO2.

Ag-impurity effects on the first- and second-order quadrupole interaction (QI) at ²³Na site in an isomorphic mixed system, Na_1−xAg_xNO₂ (x=0, 0.0084, 0.026, 0.079, 0.094, 0.16), have been investigated by employing ²³Na (I=3/2) magic angle spinning nuclear magnetic resonance (MAS NMR) technique. The central transition (CT) and satellite transition (ST) are simultaneously observed with this system. From the spectral analysis, the quadrupole parameter and its distribution width are obtained as a function of Ag concentration. From the intensity loss of CT MAS centerband and of the envelope function of ST MAS sidebands due to impurities, the range of their influence on the second- and first-order QI is estimated. The estimated ranges contain the second and first neighbouring Na sites from the resonating ²³Na nucleus for the first- and second-order QI, respectively.     

Structure of Ag(111)-p(4 x 4)-O: no silver oxide

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.     

Nitrogen-14 nuclear quadrupole resonance (NQR): dramatic sensitivity enhancement by large and fast temperature lowering

We have observed that, when going rapidly from ambient temperature down to liquid nitrogen temperature, the nitrogen-14 NQR signal (for transitions involving the m=0 spin state, nitrogen-14 being a quadrupolar nucleus of spin I=1) is increased by a factor of ca. 10(2). While Boltzmann statistics cannot explain this enhancement, the strong temperature dependence of the quadrupolar interaction is very likely to be at the origin of this phenomenon. Indeed, the quadrupolar Hamiltonian becomes time dependent and is prone to induce transitions toward the spin state associated with m=0. Its binding and slow relaxing properties result in a durable increased population and consequently in an increased intensity of NQR lines originating from the state m=0.     

Secondary signals in two-frequency nuclear quadrupole resonance on (14)N nuclei with I=1

Our experimental and theoretical studies show that using two-frequency excitation of (14)N nuclei it is possible to observe secondary NQR signals at one of the three possible transitions due to irradiation of another adjacent transition. As a result of the pulse sequence applied to the adjacent transition the spin-echo signals on the detected transition are observed after essential time interval from the initial single pulse on this frequency. Experiments have been performed on the (14)N nuclei in the sodium nitrite (NaNO(2)) and the military explosive hexahydro-1,3,5-trinitro-s-triazine C(3)H(6)N(6)O(6) (RDX).     

Level Mixing Resonance Spectroscopy (LEMS)— a novel probe of non-linear nuclear quadrupole resonance

LEMS is discussed for the case of a nuclear spin experiencing a static EFG (V_zz) and an external magnetic field (B) applied nearly colinear to V_zz). It is shown that the nature of resonances at level crossings strikingly parallels those encountered in conventional NQR with the important difference that non-linear effects involving multiphoton transitions (Δm > 1) are readily observed in LEMS because of large equivalent RF fields possible. The linewidth of these resonances are power-broadened and can be continuosly tuned by merely changing the angle between V_zz and B.